The present invention relates to a device for anchoring a probe in a well by spreading mobile anchorage arms which are applied against the walls.
An anchorage device of the aforementioned type as described in, for example, French Patent No. 2,548,727 and corresponding to U.S. Pat. No. 4,616,703, wherein at least one spring is provided, with a rod being driven in a translatory motion by expansion of the spring. Means are provided for transforming the translational movement of the rod into a pivoting movement of the anchorage arm, and means are provided for intermittently immobilizing the rod in a position in which the spring is compressed, with the immobilization means comprising a bolt adapted to be engaged in a radial recess of the rod in the compressed position of the spring and hydraulic means for moving the bolt, of an anchorage arm, and means are provided for intermittently immobilizing the rod in a position in which the spring is compressed, with the immobilization means comprising a bolt adapted to be engaged in a radial recess of the rod in the compresed position of the spring and hydraulic means for moving the bolt.
The hydraulic means may comprise a cavity formed in the body of the apparatus, a head fast with the bolt in translation and adapted to slide into the cavity, and a hydraulic circuit for intermittently applying unequal pressures to the two opposite faces of the head, with one of the two pressures being equal to the pressure prevailing in the well at the chosen depth where the apparatus is immobilized. The application of the two unequal pressures is provided, for example, by means of an electrovalve.
Since the device is most often used at a depth of several hundred meters where the pressure is high, the force to which the bolt is subjected because of the differential pressure applied to the piston is considerable and permits a very reliable and very clean tripping of opening of the arms.
However, it has been discovered that accidental tripping could occur although the electrovalve is in a closed position and isolates the bolt from the well pressure. This can be attributed to sealing defects which place the hydraulic fluid of the bolt control circuit unexpectedly at an equal pressure with the pressure prevailing in the well and causes the bolt to recoil.